Our objectives in this proposed research are to try and improve the protection of the myocardium during and immediately after cardiac surgery. This includes the development of a new simple pusatile pump system which can be adapted to a standard, clinically-available roller pump. We are particularly interested in trying to develop a method that will permit safe induced anoxic arrest for periods up to two hours. This will include not only a systematized evaluation of current and new cardioplegic agents in an in vitro cat heart preparation and in an in situ canine heart preparation, but a very critical look at the reinfusion period following the anoxic arrest. The potential protection offered by various cardioplegic agents and the manipulation of the reinfusion period will be evaluated primarily with the use of ventricular function, light and electron microscopy, regional coronary flow using radioactive microspheres, and continuous monitoring of myocardial pCO2 and pO2 using a mass spectrometer. We are anxious to continue with our previous experience in monitoring pO2 and pCO2 in patients undergoing induced anoxic arrest for aortic valve replacement. We have previously demonstrated the close correlation between intramyocardial ST-segment changes and myocardial pCO2 changes, and we plan to use an intramyocardial electrode in combination with atrial pacing to evaluate in the operating room the severity of questionable coronary occlusive lesions.